Question

If Sn =3n² +n, find the A. P.

Answer 1

Sn =3n2+n

put n = 1,

S1 =3(1)2+1=4 = a1

put n = 2,

S2 =3(2)2+2=12+2=14

put n = 3,

S3 =3(3)2+3=27+3=30

and so on.....

Now, a2 = S2 - S1 =14-4=10

a3 = S3 - S2 =30-14=16

Thus, A.P. = 4,10,16....

Answer 2

HEY mate here is your answer.

hope it helps you.